Bibliography

Dependence of Relativistic Electron Precipitation in the Ionosphere on EMIC Wave Minimum Resonant Energy at the Conjugate Equator

Abstract We investigate relativistic electron precipitation events detected by POES in low-Earth orbit in close conjunction with Van Allen Probe A observations of EMIC waves near the geomagnetic equator. We show that the occurrence rate of > 0.7 MeV electron precipitation recorded by POES during those times strongly increases, reaching statistically significant levels when the minimum electron energy for cyclotron resonance with hydrogen or helium band EMIC waves at the equator decreases below ≃ 1.0 − 2.5 MeV, as expected from quasi-linear theory. Both hydrogen and helium band EMIC waves can be effective in precipitating MeV electrons. However, > 0.7 MeV electron precipitation is more often observed (at statistically significant levels) when the minimum electron energy for cyclotron resonance with hydrogen band waves is low (Emin = 0.6 − 1.0 MeV), whereas it is more often observed when the minimum electron energy for cyclotron resonance with helium band waves is slightly larger (Emin = 1.0 − 2.5 MeV), indicative of warm plasma effects for waves approaching the He+ gyrofrequency. We further show that most precipitation events had energies > 0.7 − 1.0 MeV, consistent with the estimated minimum energy (Emin ∼ 0.6 − 2.5 MeV) of cyclotron resonance with the observed EMIC waves during the majority of these events. However, 4 out of the 12 detected precipitation events cannot be explained by electron quasi-linear scattering by the observed EMIC waves, and 12 out of 20 theoretically expected precipitation events were not detected by POES, suggesting the possibility of nonlinear effects likely present near the magnetic equator, or warm plasma effects, and/or narrowly localized bursts of EMIC waves. This article is protected by copyright. All rights reserved.

Zhang, X.-J.; Mourenas, D.; Shen, X.-C.; Qin, M.; Artemyev, A.; Ma, Q.; Li, W.; Hudson, M.; Angelopoulos, V.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 04/2021

YEAR: 2021     DOI: https://doi.org/10.1029/2021JA029193

EMIC waves; relativistic electron precipitation; minimum resonant energy; Van Allen Probes; POES; Radiation belts

Statistical Dependence of EMIC Wave Scattering on Wave and Plasma Parameters

Abstract A recent statistical study (Qin et al., 2018, https://doi.org/10.1029/2018JA025419) has suggested that not all electromagnetic ion cyclotron (EMIC) waves can scatter relativistic electrons. However, knowledge of the factors that influence the EMIC wave scattering efficiency is still limited in observations. In our study, we perform 6 years of analysis of data from 2013 to 2018, with relativistic electron precipitation (REP) observed by POES and EMIC wave observations from Van Allen Probes. The coincidence occurrence rate between EMIC waves and relativistic electron precipitation events is about 34\%. Proportion of different bands of EMIC wave events that are associated with REP is as follows: H+ band and He+ band waves occurring simultaneously >H+ band >He+ band occurrence, same as in our previous study (Qin et al., 2018, https://doi.org/10.1029/2018JA025419). It is also found that the coincidence occurrence rate of EMIC wave events and REP events increases with respect to increased background plasma density, with increases in the ratio of plasma frequency to local gyrofrequency, increasing EMIC wave power and when the wave frequency approaches the gyrofrequency. The dependence on background electron density is stronger than the dependence on the ratio of plasma frequency to gyrofrequency. The coincidence occurrence rate decreases as the magnetic field increases between 120 and 270 nT, consistent with a previous study. These results are critical for better understanding and predicting the REP into the upper atmosphere due to EMIC waves.

Qin, Murong; Hudson, Mary; Millan, Robyn; Woodger, Leslie; Shen, Xiaochen;

Published by: Journal of Geophysical Research: Space Physics      Published on:

YEAR: 2020     DOI: 10.1029/2020JA027772

EMIC waves; relativistic electron precipitation; coincidence occurrence rate; parametric dependence; Van Allen Probes

Statistical investigation of the efficiency of EMIC waves in precipitating relativistic electrons

Electromagnetic ion cyclotron (EMIC) waves have been proposed to cause Relativistic Electron Precipitation (REP). In our study, we carry out 4 years of analysis from 2013 to 2016, with relativistic electron precipitation spikes obtained from POES satellites and EMIC waves observation from Van Allen Probes. Among the 473 coincidence events when POES satellites go through the region conjugate to EMIC wave activity, only 127 are associated with REP. Additionally, the coincidence occurrence rate is about 10\% higher than the random coincidence occurrence rate, indicating that EMIC waves and relativistic electrons can be statistically related, but the link is weaker than expected. H+ band EMIC waves have been regarded as less important than He+ band EMIC waves for the precipitation of relativistic electrons. We demonstrate that the proportion of H+ band EMIC wave events that are associated with REP (22\% to 32\%) is slightly higher than for He+ band EMIC wave activity (18\% to 27\%). An even greater proportion (25\% to 40\%) of EMIC waves are accompanied by REP events when H+ band and He+ band EMIC waves occur simultaneously.

Qin, Murong; Hudson, Mary; Millan, Mary; Woodger, Leslie; Shekhar, Sapna;

Published by: Journal of Geophysical Research: Space Physics      Published on: 06/2018

YEAR: 2018     DOI: 10.1029/2018JA025419

causally related; coincidence occurrence rate; efficiency; EMIC wave; random coincidence occurrence rate; relativistic electron precipitation; Van Allen Probes

Investigation of EMIC wave scattering as the cause for the BARREL January 17, 2013 relativistic electron precipitation event: a quantitative comparison of simulation with observations

Electromagnetic ion cyclotron (EMIC) waves were observed at multiple observatory locations for several hours on 17 January 2013. During the wave activity period, a duskside relativistic electron precipitation (REP) event was observed by one of the BARREL balloons, and was magnetically mapped close to GOES-13. We simulate the relativistic electron pitch-angle diffusion caused by gyroresonant interactions with EMIC waves using wave and particle data measured by multiple instruments on board GOES-13 and the Van Allen Probes. We show that the count rate, the energy distribution and the time variation of the simulated precipitation all agree very well with the balloon observations, suggesting that EMIC wave scattering was likely the cause for the precipitation event. The event reported here is the first balloon REP event with closely conjugate EMIC wave observations, and our study employs the most detailed quantitative analysis on the link of EMIC waves with observed REP to date.

Li, Zan; Millan, Robyn; Hudson, Mary; Woodger, Leslie; Smith, David; Chen, Yue; Friedel, Reiner; Rodriguez, Juan; Engebretson, Mark; Goldstein, Jerry; Fennell, Joseph; Spence, Harlan;

Published by: Geophysical Research Letters      Published on: 12/2014

YEAR: 2014     DOI: 10.1002/2014GL062273

BARREL; EMIC waves; GOES; pitch angle diffusion; RBSP; relativistic electron precipitation; Van Allen Probes